TWO STROKE ENGINE

Abstract

 The invention relates to a two stroke internal combustion engine comprising:
- a cylinder with an inlet port and outlet port arranged in the cylinder wall;
- a piston movable within the cylinder between a top position and a bottom position, which piston has a top part with a first diameter corresponding to the inner diameter of the cylinder and which piston has a bottom part with a second diameter, which second diameter is smaller than the first diameter;
- a top seal arranged between the top part of the piston and the cylinder wall;
- a bottom seal arranged between the bottom part of the piston and the cylinder wall; and
- a bypass channel connecting a bottom part of the cylinder space with a top part of the cylinder space,

wherein the bypass channel substantially envelopes the cylinder, having inlet openings and outlet openings extending through the cylinder wall into the cylinder and wherein the inlet openings and outlet openings are distributed over the circumference of the cylinder wall and are arranged in an annular inlet configuration and an annular outlet configuration.

Description

[0001] The invention relates to a two stroke internal combustion engine comprising:

• a cylinder with an inlet port and outlet port arranged in the cylinder wall;
• a piston movable within the cylinder between a top position and a bottom position, which piston has a top part with a first diameter corresponding to the inner diameter of the cylinder and which piston has a bottom part with a second diameter, which second diameter is smaller than the first diameter;
• a top seal arranged between the top part of the piston and the cylinder wall;
• a bottom seal arranged between the bottom part of the piston and the cylinder wall; and
• a bypass channel connecting a bottom part of the cylinder space with a top part of the cylinder space.

[0002] Such a two stroke internal combustion engine is for example known from WO 2007/142512. With this known two stroke internal combustion engine, the pumping action for sucking in air with fuel is not done via the crankcase, which is typical for a two-stroke engine, but via the space created around the bottom part of the piston, due to the reduced second diameter. Oil is present in the crankcase to lubricate different parts of the engine and it is no longer necessary to add oil to the fuel for operation of the engine.

[0003] With such a two stroke internal combustion engine, according to WO 2007/142512 it is required that both the top of the piston is sealed to the cylinder wall, as well as the bottom part of the piston, to get a properly sealed pumping chamber around the bottom part of the piston. Without such a sealing, in particular without the bottom sealing, the pumping chamber would be in fluid connection with the crankcase. This would reduce the pumping volume and would reduce the pumping efficiency.

[0004] Therefore, the known two stroke internal combustion engine is provided with a piston having a top part with a first diameter corresponding to the inner diameter of the cylinder and having a bottom part with a second diameter, which second diameter is smaller than the first diameter. The cylinder wall also has a reduced diameter at the bottom, such that a seal can be arranged between this bottom part of the piston and the bottom cylinder wall.

[0005] It is an object of the invention to further improve a two stroke internal combustion engine.

[0006] This object is achieved with a two stroke internal combustion engine according to the preamble, which is characterized in that the bypass channel substantially envelopes the cylinder, having inlet openings and outlet openings extending through the cylinder wall into the cylinder and wherein the inlet openings and outlet openings are distributed over the circumference of the cylinder wall and are arranged in an annular inlet configuration and an annular outlet configuration.

[0007] The annular outlet configuration is preferably arranged closer to the top position of the piston than the annular inlet configuration.

[0008] With the bypass channel substantially enveloping the cylinder in combination with the annular configuration of inlet openings and outlet openings, there is an optimal flow of air-fuel mixture from the inlet port under the top part of the piston resulting in an increased filling ratio of the space underneath the piston.

[0009] Then when the air-fuel-mixture is compressed and the top surface is moved below the annular outlet configuration, the compressed air-fuel-mixture can flow from underneath the piston, via the bypass channel, via the annular outlet configuration and flow into the cylinder space above the piston.

[0010] Because the compressed air-fuel-mixture flows via the annular outlet configuration into the cylinder space from virtual all directions, an improved filling ratio of the cylinder space is achieved.

[0011] In a preferred embodiment of the invention the outlet port extends through and is isolated from the annular outlet configuration.

[0012] Accordingly, the annular outlet configuration is interrupted by the outlet port. As a result, the compressed air-fuel-mixture flows radially into the cylinder space above the piston, while the exhaust gases flow out of the cylinder space via the outlet port. Due to the shape of the exhaust, which typically has some kind of expansion chamber. The air-fuel-mixture is stopped from directly flowing out via the outlet port by a pulse generated by the expansion chamber.

[0013] In another preferred embodiment, the top part of the piston is provided along the circumference with a depending shield for closing the outlet port, which shield extends parallel and at a distance of the bottom part of the piston.

[0014] The depending shield, will close the outlet port, when the top part of the piston has past the outlet port. This ensures, that fresh air-fuel-mixture from the inlet port does not directly flow to the outlet port. Furthermore, it allows for a longer compression stroke of the air-fuel-mixture below the top part of the piston. Due to the compression, the mixture will flow at a higher speed via the bypass channel into the cylinder space, resulting in more turbulence and accordingly a better mixture of air and fuel.

[0015] In another embodiment of the engine according to the invention the inlet port debouches in the annular inlet configuration.

[0016] In yet another embodiment of the engine according to the invention a one-directional valve, such as a reed valve, is arranged in front of the inlet port.

[0017] The one-directional valve allows for intake of the air-fuel-mixture and then compression of said mixture without pushing the mixture out via the inlet port. It also allows for a pressure build up in the intake port, wherein the average pressure in the intake port is higher than the ambient pressure.

[0018] In a further embodiment of the engine according to the invention, the top part of the piston comprises at least two circumferential grooves and wherein the top seal comprises at least two rings arranged each in one of the circumferential grooves.

[0019] Preferably, the piston is hollow and has an access opening in the bottom and wherein at least one channel is arranged between the internal space of the piston and the circumferential surface of the top part of the piston between the at least two circumferential grooves.

[0020] Oil spray present in the crankcase can easily reach the piston, condense and penetrate, via the access opening, the plurality of channels due to the pressure in the crankcase, such that a small amount of oil is fed to the top seal ensuring proper sealing and lubrication of the piston relative to the cylinder wall.

[0021] In another preferred embodiment of the engine according to the invention the cylinder comprises a cylinder head arranged at the top of the cylinder to close off one end of the cylinder and a cylinder foot arranged at the bottom of the cylinder, wherein the cylinder foot is provided with an opening with a diameter corresponding to the second diameter.

[0022] Preferably, the bottom seal is arranged in the cylinder foot.

[0023] Typically, a cylinder of a internal combustion engine is build out of several parts, one of which is the cylinder head. This enables a cost effective manufacturing of the cylinder. The cylinder head can for example be cast, while the cylindrical wall can be made from a wear resistant material. In line herewith, the cylinder according to the invention also has a cylinder foot, which provides a body in which the bottom seal can be arranged and which can be adapted to the reduced second diameter of the bottom part of the piston.

[0024] In yet another embodiment of the engine according to the invention, the bottom seal is arranged in the cylinder wall.

[0025] The seal of the known engine is provided in a conventional way by arranging one or more circumferential grooves in the bottom part of the piston and with rings arranged in the circumferential grooves.

[0026] A disadvantages of this arrangement is that the overall height of the engine is considerable, as the cylinder height is at least the distance between the top position and the bottom position of the piston increased with the distance between the top seal and the bottom seal. This cylinder height is required as both the top seal and the bottom seal need to be in contact with the cylinder wall at all times.

[0027] By arranging the bottom seal in the cylinder wall, instead of in the piston as is known in the prior art, the pumping chamber, defined between the cylinder wall and the bottom part of the piston is still sealed, while the overall height of the engine is reduced considerably. With the engine according to the invention, the cylinder height is only the distance between the top position and the bottom position of the piston increased with some addition height for arranging the bottom seal in the cylinder wall.

[0028] In a preferred embodiment of the engine according to the invention, the cylinder wall comprises on the inner wall at least one circumferential groove and the bottom seal comprises at least one ring arranged in the at least one circumferential groove.

[0029] Typical sealing rings, known in the prior art are arranged on the piston in a groove and are compressed during assembly, such that the sealing rings exert a radially outward directed force. However, with the at least one ring arranged in the at least one circumferential groove according to the invention, the ring needs to be expanded during assembly and will exert a radially inward directed force, such that the ring is clamped around the piston and provides a sealing in combination with the circumferential groove, in which the ring is positioned.

[0030] In another embodiment of the engine according to the invention, the length of the bottom part of the piston is larger than the distance between the top position and the bottom position of the piston.

[0031] By having the length of the bottom part of the piston being larger than the stroke of the piston, the distance between the top position and the bottom position, it is ensured that the bottom seal can always be in contact with the piston.

[0032] In yet another preferred embodiment of the engine according to the invention, the combined volume of the bypass channel and the inlet port is larger than the cylinder volume.

[0033] This ensures that sufficient air-fuel-mixture is already present inside of the engine, i.e. past the one-directional valve, for the next combustion stroke. Thus, the filling of the cylinder space is not restricted by any restrictions in the inlet path of the engine.

[0034] In still a further preferred embodiment of the engine according to the invention, the bottom part of the piston is provided with a friction reducing coating.

[0035] As the bottom seal will have a sliding contact with the bottom part of the piston, a friction reducing coating contributes to smooth running of the engine and increasing the fuel efficiency as the internal friction will be reduced by this coating.

[0036] These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figures 1, 2, 3 and 5 show cross-sectional views of an embodiment of an engine according to the invention in different positions.

Figure 4 shows a cross-sectional view of the engine in the position of figure 3.

Figure 6 shows a perspective view of a piston for the engine according to the invention.

Figure 7 shows a cross-sectional view of a detail of the tengine of figure 1.

Figure 8 shows a side view of the detail of figure 7.

Figure 9 shows a top view of a cylinder according to the invention.

Figure 1 shows a cross-sectional view of an embodiment 1 of an engine according to the invention. The engine 1 has a cylinder 2 with a cylinder head 3 and a cylinder foot 4. The cylinder 2 is provided with an inlet port 5 and an outlet port 6. The inlet port 5 is connected to a one-directional valve 7, a carburetor 8 having a gas valve 9 and a fuel supply line 10, and an air filter 11.

[0037] The outlet port 6 is connected to an exhaust muffler 12.

[0038] Furthermore, a bypass channel 23 is provided (see figure 4) having inlet openings 30 and outlet openings 31 extending through the cylinder wall into the cylinder 2. The inlet openings 30 and outlet openings 31 are distributed over the circumference of the cylinder wall and are arranged in an annular inlet configuration and an annular outlet configuration.

[0039] Within the cylinder 2, a piston 13, 14 is movably arranged. The piston 13, 14 has a top part 13 provided with two circumferential grooves. This top part 13 has a first diameter, which corresponds to the diameter of the cylinder 2. The piston 13, 14 has further a bottom part 14 with a reduced second diameter, such that a pumping chamber 15 is provided between the bottom part 14 and the cylinder 2. To ensure sealing of this pumping chamber, the cylinder foot 4 is provided with an opening 17 having two circumferential grooves 16 for seating sealing rings. The diameter of the opening 17 corresponds to the second diameter of the bottom part 14 of the piston 13, 14.

[0040] The piston 13, 14 is connected via a drive rod 18 to a crankshaft 19 housed in a crankshaft casing 20.

[0041] In the position of the engine shown in figure 1, a space 21 is present between the top part 13 of the piston and the cylinder head 3, in which an air-fuel mixture just has been ignited by the spark plug 22. As a result, the piston 13, 14 will be pushed downward, causing the crankshaft 19 to rotate and driving for example a wheel of a bike (not shown).

[0042] Furthermore, a crankshaft casing venting tube 50 is provided between the crankshaft casing 20 and an oil separator 51. This oil separator 51 vents air via a filter 52 arranged on the top, while oil is drained at the bottom and fed back via channel 53 to the crankshaft casing 20. A valve 54 arranged in the venting tube 50 allows one to adjust the pressure in the crankshaft casing 20 and accordingly how much oil is supplied to the sealing rings in the grooves 16. The pressure may be either controlled manually or automatically. A higher pressure results in a higher rotational speed and increased oil thickness or viscosity.

[0043] Figure 2 shows the position of the engine 1, in which the piston 13, 14 has moved further down, such that a direct connection arises between the space 21 and the outlet port 6. Due to the combustion of the air-fuel mixture, the gases G, will flow out via the outlet port 6.

[0044] At the same time, the air-fuel mixture F present in the pumping chamber 15 will be compressed, as the one-directional valve 7 will close off the inlet port 5.

[0045] In figure 3 and figure 4, the piston 13, 14 has reached the bottom position. In this position, the air-fuel mixture F compressed in the pumping chamber 15 will be able to flow from the pumping chamber 15 via the inlet openings 30, bypass channel 23 and the outlet openings 31 to the space 21.

[0046] From this position, shown in figures 3 and 4, the piston 13, 14 will start to move up, such that the outlet port 6 is again closed off by the top part 13 of the piston, as well as a shield 24 arranged to the top part 13. (see figure 5). As soon as the outlet port 6 is closed, the air-fuel mixture F will be compressed in the space 21, such that it can be ignited by the spark plug 22 and the steps as described above are repeated.

[0047] When the piston 13, 14 moves up the outlet openings 31 of the bypass channel 23 will be closed off and a low pressure will be generated in the pumping chamber 15. As a result of the low pressure, the one-directional valve 7 will open and an air-fuel mixture F can be sucked into the pumping chamber 15.

[0048] As is clear from figure 4, the piston 13, 14 is hollow having an access opening 25 at the bottom, such that oil spray O can enter the inside of the piston 13, 14. At the top part 13, the piston 13, 14 is provided with a number of grooves 26 via which the oil spray O can enter for lubrication of rings arranged in these grooves 26.

[0049] Furthermore clear from this figure 4, is that the circumferential grooves 26 are arranged in the cylinder foot 4 and accommodate sealing rings, which provide an inwardly directed spring force on the bottom part 14 of the piston 13, 14 for sealing.

[0050] As furthermore clear from this figure 4, is that the height of the cylinder is mainly determined by the stroke of the piston 13, 14 in the cylinder 2 and the space required in the cylinder foot 4 for providing the sealing means comprising the circumferential grooves 16 and the rings accommodated therein.

[0051] As the bottom part 14 of the piston 13, 14 extends past the sealing means 16 into the crankshaft housing 20, some oil spray O will deposit on the outer wall of the bottom part 14, which will contribute to lubricating the sealing means 16.

[0052] Figure 6 shows a perspective view of a piston 40 for the engine according to the invention. The piston 40 has a top part 41 with a diameter corresponding to the inner diameter of the cylinder and a bottom part 42 with a smaller diameter. The top part 41 has two circumferential grooves 43 for seating sealing rings. Between the two grooves 43 an opening 44 of a channel is positioned. This channel connects the opening 44 with the hollow interior and open bottom of the piston 40.

[0053] A shield 45 depends from the top part 41 and is used for closing the outlet port of the cylinder.

[0054] At the bottom of the piston 40 a through hole 45 is arranged for seating the gudgeon pin 46. The gudgeon pin 46 connects the piston 40 to the drive rod. Because the through hole 45 is arranged in the piston as a non-composite hole, i.e. made in one single material, the forces of the drive rod are optimally transferred on to the piston 40.

[0055] A cover plate 47 is slided in axial direction into the slot 48 in front of the hole 45, to prevent the gudgeon pin 46 from moving out of the through hole 45.

[0056] The opening 44 is provided for providing oil between the seals arranged in the grooves 43. By controlling the pressure in the crankcase, which is in direct contact via the channel with the opening 44, the amount of oil supplied to the opening 44 can be controlled.

[0057] Figure 7 shows a detail of the sealing rings 55 arranged in the groove 16 in the cylinder wall 56. The sealing rings 55 are spaced apart by a spacer ring 57.

[0058] Each ring 55 has a slanting inner surface 58, which ensures that any excess oil is moved downwardly towards the crankshaft casing 20. Furthermore, the slanting surface 58 contributes in generating an air cushion between the sealing rings 55, which will provide a bearing for the piston 14, when the piston 14 moves up and down.

[0059] Figure 8 shows a side view of the rings 55 and spacer ring 57. The lock 59, 60 present in the sealing rings 55 is mirrored with respect to the two sealing rings 55. This further contributes in providing an air cushion.

[0060] Figure 9 shows a top view of a similar embodiment 100, showing cylinder head 102, with inlet openings 130 and outlet openings 131 in connection with bypass channel 123, as well as outlet port 106.

Claims

1. Two stroke internal combustion engine comprising:

- a cylinder with an inlet port and outlet port arranged in the cylinder wall;

- a piston movable within the cylinder between a top position and a bottom position, which piston has a top part with a first diameter corresponding to the inner diameter of the cylinder and which piston has a bottom part with a second diameter, which second diameter is smaller than the first diameter;

- a top seal arranged between the top part of the piston and the cylinder wall;

- a bottom seal arranged between the bottom part of the piston and the cylinder wall; and

- a bypass channel connecting a bottom part of the cylinder space with a top part of the cylinder space,
characterized in that
the bypass channel substantially envelopes the cylinder, having inlet openings and outlet openings extending through the cylinder wall into the cylinder and wherein the inlet openings and outlet openings are distributed over the circumference of the cylinder wall and are arranged in an annular inlet configuration and an annular outlet configuration.

2. Engine according to claim 1, wherein the annular outlet configuration is arranged closer to the top position of the piston than the annular inlet configuration.

3. Engine according to claim 1 or 2, wherein the outlet port extends through and is isolated from the annular outlet configuration.

4. Engine according to any of the preceding claims, wherein the top part of the piston is provided along the circumference with a depending shield for closing the outlet port, which shield extends parallel and at a distance of the bottom part of the piston.

5. Engine according to any of the preceding claims, wherein the inlet port debouches in the annular inlet configuration.

6. Engine according to any of the preceding claims, wherein a one-directional valve, such as a reed valve, is arranged in front of the inlet port.

7. Engine according to any of the preceding claims, wherein the top part of the piston comprises at least two circumferential grooves and wherein the top seal comprises at least two rings arranged each in one of the circumferential grooves.

8. Engine according to claim 7, wherein the piston is hollow and has an access opening in the bottom and wherein at least one channel is arranged between the internal space of the piston and the circumferential surface of the top part of the piston between the at least two circumferential grooves.

9. Engine according to any of the preceding claims, wherein the cylinder comprises a cylinder head arranged at the top of the cylinder to close off one end of the cylinder and a cylinder foot arranged at the bottom of the cylinder, wherein the cylinder foot is provided with an opening with a diameter corresponding to the second diameter.

10. Engine according to claim 9, wherein the bottom seal is arranged in the cylinder foot.

11. Engine according to any of the preceding claims, wherein the combined volume of the bypass channel and the inlet port is larger than the cylinder volume.

Drawing